1. Field of the Invention
The present invention relates generally to a pressure cap removably fitted to an upper end of a tank of a heat exchanger for cooling automobile engine cooling water.
2. Description of the Related Art
A filler neck for water supply is disposed at the upper end of the tank of the heat exchanger for cooling the automobile engine cooling water. A pressure cap shown in FIG. 8 is removably fitted to the filler neck opening. A pressure valve 6 is suspended on the central underside of a cap body 3 by way of a suspension member 34 and a retainer 33, with a negative pressure valve 22 being provided centrally of the pressure valve 6. For the pressure valve 6, a tapered tubular connection metal fitting 38 is joined at its outer periphery to the inner peripheral surface of a pot-shaped valve body 14 having a central insertion hole, with its extremity being vertically displaceably guided by the retainer 33 in the shape of a temple bell.
A seal plate 15 is attached via a stem guide 28 to the under side of the valve body 14. A stem 35 is inserted into the stem guide 28 and the negative pressure valve 22 is secured to an extremity of the stem 35. Between the upper head of the stem 35 and the valve body 14 there is interposed a negative pressure spring 30. A seat plate 36 and a plate spring 31 are disposed at the upper end of the retainer 33, with a seal plate 32 clamped therebetween. A pressing spring 4 at its upper end is seated on the seat plate 36 and at its lower end is seated on the connection metal fitting 38. Reference numeral 40 denotes an aperture.
A flanged portion is formed at the upper edge of the filler neck of the heat exchanger tank that is fitted with the thus constructed pressure cap, the flanged portion having a locking cam face on which is locked a claw 41 of the cap body 3. The pressure valve 6 is then seated on the valve seat of the filler neck for press fitting.
When the internal pressure of the tank increases as a result of a rise of the cooling water temperature by the operation of the engine, the pressure valve 6 is raised against a spring force of the pressing spring 4 so that steam and high temperature cooling water are led into a surge tank through a pipe coupled to the filler neck. When the cooling water temperature drops as a result of halt of the engine, the interior of the tank goes negative allowing the negative pressure valve 22 to be displaced downward so that the cooling water within the surge tank can flow back into the interior of the heat exchanger tank by way of the aperture 40.
The conventional pressure cap involved a lot of constituent elements leading to an increased number of assembly steps, thus imposing size limitations. In addition, the presence of the pressure cap projecting from the upper end of the heat exchanger to a large extent placed restrictions on the layout upon the mounting of the heat exchanger on the motor vehicle.
It is therefore the object of the present invention to provide a compact pressure cap with a reduced number of constituent elements.
To attain the above object, according to an aspect of the present invention there is provided a pressure cap comprising a cap body removably fitted to a filler neck for water supply disposed at an upper end of a tank of a heat exchanger; and a pressure valve disposed on an inner surface of the cap body, the pressure valve being urged downward by a pressing spring, the pressure valve being releasably seated on a valve seat of the filler neck; the cap body including a cylindrical outer peripheral portion and a top closure portion that are integrally molded of resin, the cap body having on its outer peripheral surface an external thread mating with an internal thread formed in an opening of the filler neck, the cap body having at its outer peripheral lower end a shoulder or an annular groove for receiving an O-ring, the cylindrical portion having an annular, inwardly flanged valve stopper formed on its inner peripheral surface, the pressure valve including a pot-shaped valve body and a seal plate disposed on the bottom outer surface, the valve body having along its outer periphery a plurality of slits for deformation that extend from its upper edge toward the bottom surface, the valve body having at its upper edge a locking rib that extends outward, the locking rib having an external diameter larger than the internal diameter at the edge of the valve stopper, the external diameter of the locking rib being smaller than the internal diameter of portions above the valve stopper, the presence of the slits allowing the upper external diameter of the valve body to resiliently be contracted and deformed so that the locking rib can be mounted above the valve stopper, the cap body being screwed such that the O-ring mounted on the shoulder or annular groove of the cap body can be press fitted on the inner peripheral surface of the filler neck.
Preferably, the cap body includes a guide tapered surface whose diameter increases from the edge of the valve stopper downward.
The valve body may have an insertion hole located centrally of its bottom. The pressure cap may further comprise a negative pressure valve consisting of a circular plate-like portion and a centrally extending stem that are integrally molded of a resin, the stem being inserted into the insertion hole of the valve body.
Preferably, the valve body is made of a molded form of a synthetic resin, the valve body including a cylindrical stem guide that is integral with the insertion hole, the stem being inserted into the stem guide.
The valve body may be screwed such that a top surface of the cap body substantially coincides with an upper end face of the filler neck.